Electroslag welding method

ABSTRACT

A method for electroslag welding of metals by a large-section electrode includes establishing a slag bath, fusing the electrode and the edges being weld-joined, filling with molten metal the inlet metal mould and the gap between the edges, and subsequently removing the inlet shrinkhead. The electrode is, in establishing the slag bath and filling with metal the inlet metal mould, fused at a rate lower than the electrode fusion rate in filling with metal the gap between the edges being weld-joined at constant electrical parameters of the electroslag welding. A brittle interlayer is formed between the inlet shrinkhead and the weld in the course of welding, and the weld is made so that it has a low electrical resistance.

FIELD OF THE INVENTION

The present invention relates to the art of welding and is specificallyconcerned with a method for electroslag welding of metals by alarge-section electrode.

DESCRIPTION OF THE PRIOR ART

There has been proposed a method for electroslag welding of copperblanks (U.S. Pat. No. 3,885,121), comprising the steps of establishingand overheating a slag bath by a nonconsumable electrode, removing thenonconsumable electrode from the overheated slag bath and replacing itby a consumable electrode, fusing the latter electrode by the heat ofthe slag bath and filling with the molten metal the inlet metal mouldand the gap between the edges being weld-joined, and subsequentlyremoving the inlet shrinkhead.

The changeover from the process of establishing and overheating the slagbath by the nonconsumable electrode to the process of welding proper bythe consumable electrode, inherent in this method, is a prolongedintermediate step which brings about a considerable loss of the heataccumulated in the slag bath and, as a result, a lack of fusion at thebeginning of the weld. Also, overheating the slag bath causes it toboil, which upsets the stability of the process.

This method necessitates the step of cutting and appropriate equipmentto remove the inlet shrinkhead from the weld joint.

Known in the art is also a method for electroslag welding by alarge-section electrode (Safonnikov A.N. Svarka metallov plastinchatymielektrodami (Metal welding by plate electrodes). Kiev, "Tekhnika", 1966,pp. 57-58), comprising the steps of establishing a slag bath by aconsumable electrode, filling by the molten metal the inlet metal mouldand the gap between the edges being weld-joined, and subsequentlyremoving the inlet shrinkhead. In this method, the rate of electrodefusion in establishing the slag bath, fusing the electrode and the edgesbeing weld-joined, and filling by the molten metal the inlet metal mouldand the gap between the edges, remains constant on condition that theelectrical parameters of the welding process are unchanged.

This method fails, however, to ensure a proper fusion of the edges beingweld-joined at the bottom of the weld, which leads to an increasedelectrical resistance of the welded contact. For a proper fusion of theedges at the bottom of the weld and a low electrical resistance weld tobe attained, a long time must be spent for heating the slag bath to theworking temperatures; in welding, e.g., aluminium, the time is as longas 3-5 min.

The term "working temperatures" is intended to denote the temperaturerange at which a stable electroslag process and a sound weld areattained.

Extended inlet metal moulds dictated by this prior art method to bringthe slag bath to the working temperatures result in a considerableover-expenditure of the electrode metal.

After a weld joint has been made by the prior art method, the inletshrinkhead is removed by mechanical, arc, etc. cutting.

SUMMARY OF THE INVENTION

The principal object of the invention is to provide a method forelectroslag welding of metals by a large-section electrode, whichensures a higher quality of the weld, improved mechanical properties ofthe weld joint as a whole, a low electrical resistance of the weldedcontacts, and simplified removal of an inlet shrinkhead by reducing theduration of heating to working temperatures and by forming a brittleinterlayer between the inlet shrinkhead and the weld.

This object is attained by a method of electroslag welding of metals bya large-section electrode, comprising the steps of establishing a slagbath, fusing an electrode and the edges being weld-joined, filling withthe metal being fused the inlet metal mould and the gap between theedges, and subsequently removing the inlet shrinkhead. According to theinvention, the electrode is in establishing the slag bath and fillingthe inlet metal mould, fused at a rate lower than the rate of its fusionin filling the gap between the edges being weld-joined at constantelectrical parameters of the electroslag welding, and a brittleinterlayer between the inlet shrinkhead and the weld is formed in thecourse of welding, the weld being made so that it has a low electricalresistance.

Such a relation between the electrode fusion rates cuts down the timefor heating the slag bath to the working temperatures and steps up theheat input in establishing the slag bath and filling the inlet metalmould with the metal. In addition, the welded contacts so produced offera low electrical resistance.

A modification of the method of the invention for electroslag welding ofmetals by a large-section electrode is one in which to establish theslag bath and to fill the inlet metal mould, an electrode metal isselected whose melting point exceeds that of the metal being welded, andto fuse the edges being weld-joined and to fill with metal the gaptherebetween. An electrode metal identical to the metal being welded isselected and is alternated with an electrode metal having a lowerelectrical resistance than does the metal being welded.

Such a selection of the electrode melting points reduces the electrodefusion rate in establishing the slag bath and filling the inlet metalmould with metal. The alternation of metals with different electricalconductivity in the electrode allows obtaining the weld metal withinterlayers offering a low electrical resistance.

In accordance with the invention, filling the inlet metal mould withmetal and forming a brittle interlayer between the inlet shrinkhead andthe weld in the course of welding are accomplished by an electrode whosemetal forms brittle intermetallic compounds with the metal being welded;such compounds allow the inlet shrinkhead to be easily separated fromthe weld without resorting to a cutting equipment.

Also, the disposition of the brittle interlayer between the inletshrinkhead and the weld in the course of welding is governed byselecting the volume of the electrode for establishing the slag bath andfilling the inlet metal mould with metal within 80-95% of the inletmetal mould volume.

Selecting the electrode volume within the above range enables the amountof reinforcement of the weld bottom to be controlled in the course ofwelding without impairing the weld quality.

The invention also provides in the electroslag welding of metals theformation of brittle interlayers between the welds of a plurality ofproducts disposed above one another and weld-joined in a single pass.

Such a welding technique allows a plurality of products to be weldedsimultaneously, raises the productive capacity of welding, and cuts downthe consumption of welding materials.

The electrode volume needed to fill the gap between the edges beingweld-joined is to be selected 10-25% greater than the volume defined bythe edges.

Such a selection of the electrode volume enables a weld with a varyingconfiguration to be obtained in the course of welding.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the process of establishing a slag bath according tothe invention;

FIG. 2 illustrates a steady-state electroslag welding process accordingto the invention;

FIG. 3 shows the appearance of a weld joint with a brittle interlayerbetween the inlet shrinkhead and the weld according to the invention;

FIG. 4 shows the appearance of the weld joint with the inlet shrink-headremoved according to the invention;

FIG. 5 shows the appearance of a plurality of products disposed oneabove another and weld-joined in a single pass according to theinvention; and

FIG. 6 illustrates a steady-state electroslag welding process and theformation of a weld with interlayers having a low electrical resistanceaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The method for electroslag welding of metals by a large-sectionelectrode according to the invention is explained by way of particularexamples of accomplishing it.

EXAMPLE 1

70×500-mm section aluminium busbars or segments 1 to be weld-joined wereplaced with a 50-mm gap on an inlet metal mould 2. A 20×60-mm sectionelectrode 3 was installed into the gap between the busbars 1 so that itcontacted the bottom of the metal mould 2. The bottom part 4 of theelectrode 3 was copper, its volume being of 80% of the volume of themetal mould 2; the melting point of the metal of the bottom part of theelectrode 3 was 1080° C.

The top part 5 of the electrode 3 was aluminium with 20×60×10-mm copperinserts 6 spaced at 100 mm from one another. The melting point of themetal of the top part 5 of the electrode was 660° C., and of the insertsit was 1080° C.

The bottom part 4 and top part 5 of the electrode 3 and the inserts 6were butt-welded. The volume of the top part 5 of the electrode 3 was10% greater than the volume defined by the edges to be weld-joined ofthe busbars 1. Moulding shoes 7 were installed at the sides of thebusbars 1 to be weld-joined, and graphite run-on plates 8 were placedatop the busbars 1.

The electrode 3 and busbars 1 were then connected to a weldingtransformer 9. Flux (not shown) was poured into the metal mould 2, andthe welding circuit was closed.

The welding conditions were as follows:

U_(no-load) =36 V;

I_(weld) =4.0 kA.

Melting down, the flux shunted the arc and gave rise to a slag bath; thebottom part of the electrode 3 started fusing. After the bottom part 4of the electrode 13 fused down, the metal mould 2 was filled by 80% withcopper, following which a 10 mm thick brittle interlayer 11 formed,consisting of compounds of the metal of the bottom part 4 of theelectrode 3 and of the metal being welded of the busbars 1, i.e. ofcopper and aluminium. During a further fusion of the electrode 3, namelyof the top part 5 thereof, the gap between the edges being-weld-joinedwas being filled. The weld thus formed had interlayers 12 ofaluminium-copper system compounds whose electrical resistance is lessthan that of the metal being welded, i.e. aluminium.

After the welding gap becomes filled with the electrode metal, thewelding current was switched off.

The inlet shrinkhead 13 was easily removed from the weld along thebrittle interlayer 11 by exposing the shrinkhead 13 to a small impactload, and then the obtained weld reinforcement was measured, whichamounted to 10 mm. The weld was free of shrinkage porosities.

Different fusion rates of the bottom part 4 and the top part 5 of theelectrode 3, attained by selected the metal of the electrode 3 so thatthe melting point of the bottom part 4 was 1080° C., and of the top part5 was 660° C., shortened the time for heating the slag bath 10 to theworking temperature by 25% as against that in the prior art method.

The weld thus produced was equivalent in mechanical properties to themetal being welded.

The electrical resistance of the welded contact was 10% lower than thatof the busbars being weld-joined.

Note: In welding assemblies other than welding contacts, the interlayers12 in the weld are not used.

The following examples of accomplishing the method for electroslagwelding in accordance with the invention were similar to Example 1; thewelding parameters are listed in the Table below, the welding conditionsbeing the same.

The weld reinforcement was in Example 2, of 3 mm; in Example 3, of 5 mm.In accomplishing the method according to Example 4, there was a large(20 mm) reinforcement at the expense of the electrode material at theweld bottom after the shrinkhead had been removed,

    ______________________________________                                                                         Volume of                                                              Volume electrode                                                              of elec-                                                                             top part                                                 Mater-        trode  in % of Melting                                  Mater-  ial of  Mater-                                                                              bottom volume  point of me-                         Ex- ial     elec-   ial of                                                                              part in                                                                              defined tal of elec-                         am- of bus- trode   elec- % of me-                                                                             by edges                                                                              trode bottom                         ple bars    bottom  trode tal mould                                                                            being weld-                                                                           part,                                No. being   part    inserts                                                                             volume joined  °C.                           ______________________________________                                        2   Magne-  Cu      --    95     125     1080                                     sium                                                                      3   Steel   Ti      --    90     120     1700                                     C .3                                                                      4   Al      Cu      Cu    75     105     1080                                 5   Al      Cu      Cu    100    130     1080                                 ______________________________________                                    

which necessitated an additional working.

In accomplishing the method according to Example 5, a decrease in thesection of the weld working part was noted at the weld bottom afterremoving the inlet shrinkhead, which was caused by some weld metal beingremoved jointly with the shrinkhead.

The time for heating the slag bath to the working temperature was inExamples 2, 4, and 5 the same as in Example 1, and in Example 3 half aslong as in the prior art method.

The welds produced in Examples 2 and 3 had a weld joint factor of 0.8and 0.9 respectively, i.e. the weld strength was respectively 80 and 90%of the strength of the metal being welded.

EXAMPLE 6

This Example is given to explain the accomplishment of the method forelectroslag welding in one pass of products disposed one above another.

Three butt joints of 50×100-mm section aluminium busbars were weldedsimultaneously.

The welding was accomplished similarly to Example 1. An electrodesection of 20×40 mm was selected. Busbars 15 and 16 to be weld-joinedwere placed atop busbars 1 with 50×50×100-mm copper spacers 14interposed between the busbars (see FIG. 5). The gap between the edgesto be weld-joined of the busbars 1, 15, and 16 was selected at 50 mm.The welding resulted in producing an integral weldment which readilyseparated into three welded busbars 1, 15, and 16 under an impact loadapplied to brittle interlayers 17 disposed at the places of installationof the spacers 14. The inlet shrinkhead 13 of the busbar 1 easilyseparated from the busbar along the brittle interlayer 11.

The reinforcement of the first weld was similar to that obtained inExample 1.

INDUSTRIAL APPLICABILITY

The invention may be used in nonferrous metallurgy, electrical,chemical, and machine-building industry in manufacturing large-sizeweldments whose components are mainly of aluminium, copper, titanium andsteel.

The invention may be particularly useful in manufacturing heavyaluminium busbars for electrolyzers used in nonferrous metallurgy.

We claim:
 1. A method for electroslag welding of metal segments by alarge-section electrode, comprising the steps of establishing a slagbath, fusing an electrode and edges of the metal segments beingweld-joined, filling with the metal being fused an inlet metal mould andthe gap between the edges of the metal segments, and subsequentlyremoving an inlet shrinkhead, wherein the improvement comprises theelectrode being, in establishing the slag bath and filling with metalthe inlet metal mould, fused at a rate lower than the electrode fusionrate in filling with metal the gap between the edges of the metalsegments being weld-joined at constant electrical parameters of theelectroslag welding, and a brittle interlayer between the inletshrinkhead and the weld being formed in the course of welding, the weldbeing made so that it has a low electrical resistance.
 2. A method asdefined in claim 1, further comprising, to establish the slag bath andto fill the inlet metal mould with metal, selecting an electrode whosemetal has a melting point exceeding the melting point of the metal beingwelded, and fusing the edges of the metal segments being weld-joined andfilling with metal the gap therebetween, and selecting an electrodemetal identical to the metal being welded and alternating it with anelectrode metal having a lower electrical resistance than the metalbeing welded.
 3. A method as defined in claim 1, wherein filling theinlet metal mould with metal and forming the brittle interlayer betweenthe inlet shrinkhead and the weld in the course of welding areaccomplished by an electrode whose metal forms brittle intermetalliccompounds with the metal being welded.
 4. A method as defined in claim1, wherein filling the inlet metal mould with metal and forming thebrittle interlayer between the inlet shrinkhead and the weld in thecourse of welding are accomplished by an electrode whose metal formsbrittle intermetallic compounds with the metal being welded, and thedisposition of the brittle interlayer between the inlet shrinkhead andthe weld in the course of welding is governed by selecting the volume ofthe electrode for establishing the slag bath and filling the inlet metalmould with metal within 80-95% of the inlet metal mould volume.
 5. Amethod as defined in claim 1, wherein producing a weld of a varyingconfiguration is controlled by selecting the volume of the electrode forfilling with metal the gap between the edges being weld-joined 10-25%greater than the volume defined by the edges.
 6. A method as defined inclaim 1, wherein the brittle interlayers are formed between the welds ofproducts disposed one above another and separated from one another byspacers whose material forms brittle intermetallic compounds with themetal being welded, the welding of a plurality of products being carriedout simultaneously in a single pass.